Silver phosphate, solubility

Silver Phosphates. Silver phosphate [7784-09-0], or silver orthophosphate, Ag3P04, is a bright yellow material formed by treating silver nitrate with a soluble phosphate salt or phosphoric acid. Silver pyrophosphate [13465-97-9], is a white salt prepared by the addition of a soluble... 

If the dissociation constant of the acid HA is very small, the anion A- will be removed from the solution to form the undissociated acid HA. Consequently more of the salt will pass into solution to replace the anions removed in this way, and this process will continue until equilibrium is established (i.e. until [M + ] x [A-] has become equal to the solubility product of MA) or, if sufficient hydrochloric acid is present, until the sparingly soluble salt has dissolved completely. Similar reasoning may be applied to salts of acids, such as phosphoric(V) acid (K1 = 7.5 x 10-3 mol L-1 K2 = 6.2 x 10-8 mol L-1 K3 = 5 x 10 13 mol L-1), oxalic acid (Kx = 5.9 x 10-2 mol L-K2 = 6.4 x 10-5molL-1), and arsenic)V) acid. Thus the solubility of, say, silver phosphate)V) in dilute nitric acid is due to the removal of the PO ion as... 

Silver phosphate (Ag3P04), [CAS 7784-09-01 yellow precipitate, by reaction of silver nitrate solution and disodium hydrogen phosphate solution, soluble in HNO3 and in NH4OH, turns dark on exposure to light. 

The deposition of silver in tissues is the result of the precipitation of insoluble silver salts, such as silver chloride and silver phosphate. These insoluble silver salts appear to be transformed into soluble silver sulfide albuminates, to bind to or form complexes with amino or carboxyl groups in RNA, DNA, and proteins, or to be reduced to metallic silver by ascorbic acid or catecholamines (Danscher 1981). The blue or gray discoloration of skin exposed to ultraviolet light in humans with argyria may be caused by the photoreduction of silver chloride to metallic silver. The metallic silver is then oxidized by tissue and bound as black silver sulfide (Danscher 1981). Bucklet et al. (1965) identified silver particles deposited in the dermis of a woman with localized argyria as being composed of silver sulfide. 

This concept also applies to salts with other types of anions. For example, the solubility of silver phosphate, Ag3P04, is greater in acid than in pure... 

According to our solubility guidelines, most phosphates are insoluble, and compounds with Ag are not listed as an exception. Therefore, silver phosphate, Ag3P04, which is used in photographic emulsions, would be insoluble. Because compounds containing Na and N03 are soluble, NaN03 is soluble. 

Deposition of silver in tissues of warmblooded animals results from precipitation of relatively insoluble silver salts, such as silver chloride and silver phosphate. These insoluble salts may be transformed into soluble silver sulfide albuminates that bind or... 

Electrochemical Process. Several patents claim that ethylene oxide is produced ia good yields ia addition to faradic quantities of substantially pure hydrogen when water and ethylene react ia an electrochemical cell to form ethylene oxide and hydrogen (206—208). The only raw materials that are utilized ia the ethylene oxide formation are ethylene, water, and electrical energy. The electrolyte is regenerated in situ ie, within the electrolytic cell. The addition of oxygen to the ethylene is activated by a catalyst such as elemental silver or its compounds at the anode or its vicinity (206). The common electrolytes used are water-soluble alkah metal phosphates, borates, sulfates, or chromates at ca 22—25°C (207). The process can be either batch or continuous (see Electrochemicalprocessing). 

With the salts of certain weak acids, such as carbonic, sulphurous, and nitrous acids, an additional factor contributing to the increased solubility is the actual disappearance of the acid from solution either spontaneously, or on gentle warming. An explanation is thus provided for the well-known solubility of the sparingly soluble sulphites, carbonates, oxalates, phosphates(V), arsenites(III), arsenates(V), cyanides (with the exception of silver cyanide, which is actually a salt of the strong acid H[Ag(CN)2]), fluorides, acetates, and salts of other organic acids in strong acids. 

The solubility of the precipitates encountered in quantitative analysis increases with rise of temperature. With some substances the influence of temperature is small, but with others it is quite appreciable. Thus the solubility of silver chloride at 10 and 100 °C is 1.72 and 21.1mgL 1 respectively, whilst that of barium sulphate at these two temperatures is 2.2 and 3.9 mg L 1 respectively. In many instances, the common ion effect reduces the solubility to so.small a value that the temperature effect, which is otherwise appreciable, becomes very small. Wherever possible it is advantageous to filter while the solution is hot the rate of filtration is increased, as is also the solubility of foreign substances, thus rendering their removal from the precipitate more complete. The double phosphates of ammonium with magnesium, manganese or zinc, as well as lead sulphate and silver chloride, are usually filtered at the laboratory temperature to avoid solubility losses. 

The method may be applied to those anions (e.g. chloride, bromide, and iodide) which are completely precipitated by silver and are sparingly soluble in dilute nitric acid. Excess of standard silver nitrate solution is added to the solution containing free nitric acid, and the residual silver nitrate solution is titrated with standard thiocyanate solution. This is sometimes termed the residual process. Anions whose silver salts are slightly soluble in water, but which are soluble in nitric acid, such as phosphate, arsenate, chromate, sulphide, and oxalate, may be precipitated in neutral solution with an excess of standard silver nitrate solution. The precipitate is filtered off, thoroughly washed, dissolved in dilute nitric acid, and the silver titrated with thiocyanate solution. Alternatively, the residual silver nitrate in the filtrate from the precipitation may be determined with thiocyanate solution after acidification with dilute nitric acid. 

C18-0073. For the following salts, write a balanced equation showing the solubility equilibrium and write the solubility product expression for each (a) silver chloride (b) barium sulfate (c) iron(H) hydroxide and (d) calcium phosphate. 

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